Honeydew and Sooty Mold from Aphids on Street Trees: City Management

A city tree dripping sticky sap (honeydew) onto roofs, cars, and driveways for 4 years, with grass dying under it during bloom, is infested with aphids or soft scale insects. The "sap" is actually honeydew—sugary waste excreted by these phloem-feeding insects. It's not toxic but creates a nuisance and promotes sooty mold.

Why City Spraying Failed

• Wrong timing: Sprays must hit crawlers/nymphs; adults are protected.
• Poor coverage: Large canopies need high-pressure equipment for full leaf coverage.
• Non-systemic products: Contact sprays wash off; don't protect new growth.
• Resistance: Repeated same-class insecticides select for resistance.

Effective Strategy: Systemic Soil Treatment

Imidacloprid (Bayer Advanced Tree & Shrub Insect Control Concentrate) applied as a soil drench/injection:

• Roots absorb insecticide; translocates to all foliage.
• Kills aphids/scales as they feed—no spray coverage needed.
• One application protects for a full growing season.
• Applied early spring (at bud break) for best uptake.
• Minimal impact on beneficial insects (no foliar residue).

Spray Options (If Systemic Not Feasible)

Contact insecticides (rotate classes to prevent resistance):

• Pyrethroids: bifenthrin (Talstar), permethrin
• Organophosphates: acephate (Orthene), chlorpyrifos (restricted)
• Carbamates: carbaryl (Sevin)
• Botanicals: pyrethrum, neem oil
• Insecticidal soaps, horticultural oils (thorough coverage essential)

Systemic foliar/spray: Acephate (Orthene) has both contact and systemic activity.

Timing

• Best: Early spring at full leaf expansion (first generation).
• Repeat if honeydew reappears (monitor with sticky traps).
• Fall treatment reduces overwintering populations.

Convincing the City

Present this plan: systemic soil treatment is cheaper, more effective, safer for public/applicators, and reduces drift complaints. Many municipalities have adopted it for street tree pest management.